Process for producing hydrocarbon-blown hard polyurethane foams

ABSTRACT

PCT No. PCT/EP97/01198 Sec. 371 Date Sep. 18, 1998 Sec. 102(e) Date Sep. 18, 1998 PCT Filed Mar. 10, 1997 PCT Pub. No. WO97/35899 PCT Pub. Date Oct. 2, 1997A process for preparing rigid expanded materials containing urethane and optionally urea and isocyanurate groups, characterised in that a polyurethane rigid foam is prepared by reacting a) an aromatic polyisocyanate with b) a polyol component with on average at least 3 hydrogen atoms which can react with isocyanates, containing 1) 30 to 80 wt. % of an aromatic amine started polyether with a molecular weight of 300 to 800 based on 70 to 100 wt. % of 1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide 2) 10 to 40 wt. % of a substantially sucrose started polyether with a molecular weight of 400 to 1,000 based on 70 to 100 wt. % of 1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide 3) 5 to 30 wt. % of a propylene glycol started polyether with a molecular weight of 500 to 1,500 based on 70 to 100 wt. % of 1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide 4) n-pentane and/or i-pentane as blowing agent 5) water 6) optional auxiliary agents and additives, wherein the sum of the wt. % of components 1), 2) and 3) is 100, is described.

BACKGROUND OF THE INVENTION

It is known that polyurethane rigid foams can be blown with low-boilingalkanes. Cyclic alkanes are used to advantage here because they make anoutstanding contribution to the thermal conductivity of the expandedmaterial due to their low gaseous thermal conductivity. Cyclopentane ispreferably used.

The beneficial properties when used as an insulator in domesticrefrigerators have to be compared with a disadvantageous commercialsituation. Thus, a specific quality of polystyrene inner container hasto be used, as a result of the solvent properties of cyclopentane.

Furthermore, cyclopentane has the disadvantage, due to its relativelyhigh boiling point of 49° C., that it condenses at low temperatures suchas are conventional during the use of polyurethane rigid foams asinsulators in domestic refrigerators. Due to the undesired condensationof the blowing agent, a reduced pressure is produced in the cells whichagain has to be offset by an elevated foam strength or increaseddensity.

Compared with the acyclic homologous pentane compounds, n-pentane andi-pentane, cyclopentane incurs higher manufacturing costs. n-pentane ori-pentane blown systems have been known for some time in the field ofpolyurethane rigid foams. However, the higher gaseous thermalconductivities, as compared with cyclopentane, which result in poorerthermal insulation capacity of the corresponding expanded systems is adisadvantage.

In addition, the solubility of n-pentane and i-pentane in polyols ismuch lower than that of cyclopentane, which has a negative effect onproduction reliability and the adhesion of the expanded material tocovering layers.

SUMMARY OF THE INVENTION

The object of the present invention was to develop a n-pentane ori-pentane blown rigid foam in which the disadvantages mentioned aboveare overcome.

Surprisingly, it has now been found that polyol formulations based onaromatic amines, sucrose and propylene glycol provide expanded materialswith good adhesive properties and lower thermal conductivities. Thesolubility of acyclic pentanes satisfies all the requirements.

DETAILED DESCRIPTION OF THE INVENTION

The present invention therefore provides a process for preparing rigidexpanded materials containing urethane and optionally isocyanurategroups, characterised in that a polyurethane rigid foam is prepared byreacting

a) an aromatic polyisocyanate with

b) a polyol component with on average at least 3 hydrogen atoms whichcan react with isocyanates, containing

1) 30 to 80 wt. % of an aromatic amine started polyether with amolecular weight of 300 to 700 based on 70 to 100 wt. % of 1,2-propyleneoxide and 0 to 30 wt. % of ethylene oxide

2) 10 to 40 wt. % of a substantially sucrose started polyether with amolecular weight of 400 to 1,000 based on 70 to 100 wt. % of1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide

3) 5 to 30 wt. % of a propylene glycol started polyether with amolecular weight of 500 to 1,500 based on 70 to 100 wt. % of1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide

4) n-pentane and/or i-pentane as blowing agent

5) water

6) optional auxiliary agents and additives,

wherein the sum of the wt. % of components 1), 2) and 3) is 100.

Amine started polyethers are preferably understood to be those based ono-toluylene diamine. This starter is preferably reacted with1,2-propylene oxide. The molecular weight of these polyethers ispreferably between 300 and 800, in particular between 500 and 600. Inpolyol formulations, the proportion of aromatic aminopolyether ispreferably 30 to 80 wt. %, in particular 35 to 70 wt. %.

The sucrose started polyethers are preferably prepared by reaction with1,2-propylene oxide; diethylene glycol, ethylene glycol or propyleneglycol in amounts of 10 to 30 wt. % is optionally used as a co-starter.

The molecular weight is preferably between 400 and 1,000, in particularbetween 500 and 600. In polyol formulations, the proportion of sucrosestarted polyethers is preferably 10 to 40 wt. %, in particular 15 to 35wt. %.

Propylene glycol started polyethers are also prepared by reaction with1,2-propylene oxide.

Propylene glycol started polyethers with a molecular weight between 500and 1,500 are preferably used, in particular between 900 and 1,100.

In polyol formulations, their proportion is preferably 5 to 30 wt. %, inparticular 15 to 25 wt. %.

By using polyol formulations in accordance with the invention, n-pentaneand i-pentane blown expanded materials with low thermal conductivitiesand good adhesion to covering layers are prepared.

The polyol formulations contain between 0.5 and 3.5 wt. %, preferablybetween 1.5 and 2.5 wt. %, of water as co-blowing agent.

Any starting components known per se may be used as polyisocyanates inthe process according to the invention.

The isocyanate components are, e.g. aromatic polyisocyanates such as aredescribed, for instance, by W. Siefkin in Justus Liebigs Annalen derChemie, 562, pages 75 to 136, for example those of the formula

    Q(NCO).sub.n

in which

n is 2 to 4, preferably 2 and

Q represents an aliphatic hydrocarbon group with 2 to 18, preferably 6to 10, carbon atoms, a cycloaliphatic hydrocarbon group with 4 to 15,preferably 5 to 10, carbon atoms, an aromatic hydrocarbon group with 8to 15, preferably 8 to 13, carbon atoms, e.g. polyisocyanates like thosewhich are described in DE-OS 2 832 253, pages 10 to 11.

Industrially readily accessible polyisocyanates are generallyparticularly preferred, e.g. 2,4 and 2,6-toluylene diisocyanate and anymixture of these isomers ("TDI), polyphenylpolymethylene polyisocyanatessuch as can be prepared by aniline/formaldehyde condensation andsubsequent phosgenation (crude "MDI") and polyisocyanates withcarbodiimide groups, urethane groups, allophanate groups, isocyanurategroups, urea groups or biuret groups ("modified polyisocyanates"), inparticular modified polyisocyanates which are derived from 2,4 and2,6-toluylene diisocyanate or from 4,4' and/or 2,4'-diphenylmethanediisocyanate.

Paraffins or fatty alcohols or dimethylpolysiloxanes as well as pigmentsor colorants, also stabilisers against the effects of ageing andweathering, plasticisers and anti-fungal or anti-bacterial substances aswell as fillers such as barium sulphate, kieselguhr, carbon black orprepared chalk, may also be incorporated.

Further examples of optionally incorporated surface active additives andfoam stabilisers, as well as cell regulators, reaction retardants,stabilisers, flame inhibiting substances, colorants and fillers as wellas anti-fungal and anti-bacterial substances for use according to theinvention and details about the use and effects of these additives aredescribed in Kunststoff-Handbuch, vol. VII, published by Vieweg andHochtlen, Carl-Hanser-Verlag, Munich, 1966, e.g. on pages 121 to 205.

When preparing a foam, according to the invention the foaming proceduremay also be performed in closed moulds. In this case the reactionmixture is introduced into a mould. Suitable mould materials are metals,e.g. aluminium, or plastics, e.g. epoxide resin. The foamable reactionmixture foams in the mould and forms the moulded item. The mould-foamingprocedure may be performed in such a way that the moulded item has acellular structure at its surface. It may also be performed, however, insuch a way that the moulded item has a solid skin and a cellular core.According to the invention, the procedure in the first case is tointroduce sufficient foamable reaction mixture into the mould for thefoam produced to just fill the mould. The mode of operation in thelast-mentioned case comprises introducing more foamable reaction mixtureinto the mould than is required to fill the interior of the mould withfoam. In the latter case, therefore, the process uses "overcharging", atype of procedure which is known. e.g. from U.S. Pat. Nos. 3,178,490 and3,182,104.

The invention also provides use of the rigid foam prepared according tothe invention as an intermediate layer for laminated elements and forfilling hollow spaces with foam in the domestic refrigerator industry.

The process according to the invention is preferably used for fillingthe hollow cavities in refrigerators and freezers with foam.

Obviously, expanded materials may also be produced by block foaming orby the double transport method which is known per se.

The rigid foams obtainable according to the invention are used, forinstance, in the building industry and for the insulation oflong-distance energy pipes and containers.

The following examples are intended to explain the invention without,however, restricting its scope.

EXAMPLE 1

(comparison example)

Formulation for polyurethane rigid foam

Component A:

    ______________________________________     75 parts by wt.             sucrose (80 wt. %) and propylene glycol (20 wt. %)             started polyether with a molecular weight             of 600 based on 1,2-propylene oxide     25 parts by wt.             propylene glycol started polyether with a molecular             weight of 1,000 based on 1,2-propylene oxide    2.5 parts by wt.             water    2.0 parts by wt.             foam stabiliser, B 8423 (from Goldschmidt)    2.0 parts by wt.             activator, Desmorapid 726b (Bayer AG)    ______________________________________

Component B:

    ______________________________________    125 parts by wt.                crude MDI (NCO content = 31.5 wt. %)    ______________________________________

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 128 parts by wt. of component B using a stirrer (1,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 2

(comparison example)

Component A

    ______________________________________     50 parts by wt.             o-toluylene diamine started polyether with a molecular             weight of 560 based on 1,2-propylene oxide     50 parts by wt.             sucrose (80 wt. %) and propylene glycol (20 wt. %)             started polyether with a molecular weight of 600 based             on 1,2-propylene oxide    2.5 parts by wt.             water    2.0 parts by wt.             foam stabiliser, B 8423 (from Goldschmidt)    2.0 parts by wt.             activator, Desmorapid 726b (Bayer AG)    ______________________________________

Component B:

    ______________________________________    141 parts by wt.                crude MDI (NCO content = 31.5 wt. %)    ______________________________________

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 141 parts by wt. of component B using a stirrer (1,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 3

(comparison example)

Component A

    ______________________________________     75 parts by wt.             o-toluylene diamine started polyether with a molecular             weight of 560 based on 1,2-propylene oxide     25 parts by wt.             propylene glycol started polyether with a molecular             weight of 1,000 based on 1,2-propylene oxide    2.5 parts by wt.             water    2.0 parts by wt.             foam stabiliser, B 8423 (from Goldschmidt)    2.0 parts by wt.             activator, Desmorapid 726b (Bayer AG)    ______________________________________

Component B:

    ______________________________________    115 parts by wt.                crude MDI (NCO content 31.5 wt. %).    ______________________________________

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 115 parts by wt. of component B using a stirrer (1,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

EXAMPLE 4

(according to the invention)

Component A

    ______________________________________     50 parts by wt.             o-toluylene diamine started polyether with a molecular             weight of 560 based on 1,2-propylene oxide     30 parts by wt.             sucrose (80 wt. %) and propylene glycol (20 wt. %)             started polyether with a molecular weight of             600 based on 1,2-propylene oxide     20 parts by wt.             propylene glycol started polyether with a molecular             weight of 1,000 based on 1,2-propylene oxide    2.5 parts by wt.             water    2.0 parts by wt.             foam stabiliser, B 8423 (from Goldschmidt)    2.0 parts by wt.             activator, Desmorapid 726b (Bayer AG)    ______________________________________

Component B

    ______________________________________    124 parts by wt.                 crude MDI (NCO content 31.5 %)    ______________________________________

100 parts by wt. of component A were mixed with 11 parts by wt. ofn-pentane and 124 parts by wt. of component B using a stirrer (1,000rpm) at 20° C. and compressed in a closed mould at 34 kg/m³.

Results

The test values given in the following Table were obtained using thefoam sheets produced in examples 1 to 4.

    ______________________________________                                         Limiting sol.           Thermal   Compression          GT/100 GT           conductivity                     strength   Adhesion polyol! of            mW/mK!    MPa! acc. to                                 MPa! acc. to                                         n-pentane in           acc. to   DIN 53421, DIN 53292                                         polyol           DIN 52616,                     10 %       to sheet mixture,    Example           24° C.                     compression                                metal    20° C.    ______________________________________    1      24        0.18       0.09      9    2      23.5      0.16       0.01     11    3      23.3      0.10       0.12     25    4      22.7      0.17       0.11     20    ______________________________________

As shown by the tests, only the foam in example 4 according to theinvention exhibits good to very good properties with regard to thermalconductivity, compression strength, adhesion to sheet metal andsolubility of pentane in the polyol formulation.

Comparison example 1 produces foam with a high thermal conductivity.Furthermore, the solubility of pentane in the polyol is not sufficient.

The foam produced in comparison example 2 has an inadequate adhesion tosheet metal; the pentane solubility is in the limiting region.

Comparison example 3 produces foam with good adhesion and good pentanesolubility in the polyol formulation; but inadequate compressionstrength.

We claim:
 1. A process for preparing rigid expanded materials containingurethane and optionally urea and isocyanurate groups, characterised inthat a polyurethane rigid foam is prepared by reactinga) an aromaticpolyisocyanate with b) a polyol component with on average at least 3hydrogen atoms which can react with isocyanates, containing1) 30 to 80wt. % of an aromatic amine started polyether with a molecular weight of300 to 800 based on 70 to 100 wt. % of 1,2-propylene oxide and 0 to 30wt. % of ethylene oxide 2) 10 to 40 wt. % of a substantially sucrosestarted polyether with a molecular weight of 400 to 1,000 based on 70 to100 wt. % of 1,2-propylene oxide and 0 to 30 wt. % of ethylene oxide 3)5 to 30 wt. % of a propylene glycol started polyether with a molecularweight of 500 to 1,500 based on 70 to 100 wt. % of 1,2-propylene oxideand 0 to 30 wt. % of ethylene oxide 4) n-pentane and/or i-pentane asblowing agent 5) water 6) optional auxiliary agents andadditives,wherein the sum of the wt. % of components 1), 2) and 3) is100.
 2. A process according to claim 1, characterised in that anaromatic amine started polyether based on o-toluylene diamine is used.3. A process according to claim 1, characterised in that a polyolcomponent with 50 to 60 wt. % of toluylene diamine started polyetherwith a molecular weight of 450 to 650 based on 1,2-propylene oxide isused.
 4. A process according to claim 1, characterised in that a polyolcomponent with 10 to 25 wt. % of a propylene glycol started polyetherwith a molecular weight of 800 to 1,200 based on 1,2-propylene oxide isused.